Modify space check to support large partitions

The embedded devices targetted by DB8 aren't nomally expected to have
partition sizes of over 2GB and false "out of space" errors can be
generated when running on larger partitions, such as on the desktop.
This change prevents those false warnings by suppressing the percentage
comparisons when over 500MB of space is available.

Open-webOS-DCO-1.0-Signed-off-by: Roger Stringer <roger.stringer@palm.com>

Change-Id: I251df0cd1465e262dd1400908e03af1c74a969d2